The objective of this project is the discovery of new types of drugs which are clinically useful against cancer. The following topics are of current interest: (1) purine nucleosides as antitumor agents and transition-state inhibitors of purine nucleoside phosphorylase, (2) new approaches towards the synthesis of the antitumor-active antibiotic neplanocin and related analogs, (3) synthesis of pyridone nucleosides as antitumor agents and potential inhibitors of cytidine triphosphate synthetase, (4) a ring-expansion approach to novel diazepinone nucleosides, (5) synthesis of diazepinone nucleoside analogs as potential antitumor agents and inhibitors of cytidine deaminase, (6) dinucleotide analogs structurally related to NAD as inhibitory agents of inosine monophosphate dehydrogenase.